Decorative architectural titanium panels and method of fabrication thereof

ABSTRACT

Titanium architectural panels ( 20 ) are provided which have recrystallized surface portions on at least the outer surface ( 22 ) thereof to give a decorative appearance to the panels ( 20 ). Surface recrystallization is obtained by subjecting the panels ( 20 ) to multiple oven heating steps (H 1 , H 2 ) with intermediate cooling steps (C 1 , C 2 ), wherein during each heating step (H 1 , H 2 ) maximum temperature ranges (T H1 , T H2 ) are established and maintained for predetermined periods. The intermediate cooling steps (C 1 , C 2 ) involve injection of an inert cooling gas (e.g., argon) into the oven to rapidly lower the temperature to minimum temperature ranges (T L1 , T L2 ). Preferably, the individual panels ( 20 ) are framed using molybdenum frame assembly ( 42 ), and are then suspended on a graphite and molybdenum hanger assembly ( 72 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is broadly concerned with decorativearchitectural panels formed of heat treated titanium, as well as methodsof forming such panels and improved fixturing permitting the heattreatment of multiple panels without warpage or distortion thereof. Moreparticularly, the invention is concerned with such panels which aresubjected to multiple, controlled heating and cooling steps so as torecrystallize the titanium surface to give a pleasing, facetedappearance; preferably, the relatively large architectural panels areindividually framed before heat treatment so as to resist unwanted edgedistortions.

[0003] 2. Description of the Prior Art

[0004] Titanium is a relatively light, silver-gray metal with a specificgravity of 0.163 lb/in³. Pure titanium has a high melting point (3035°F.) and a lower coefficient of expansion and lower thermal conductivitythan either steel or aluminum alloys. Its modulus of elasticity(1.1×10¹¹ Pa) is midway between that of steel and aluminum.

[0005] Titanium is allotropic, and up to a temperature of 1625° F.,titanium atoms are in a hexagonal close-packed alpha crystal array. Whentitanium is heated above the transition temperature of 1625° F., theatoms rearrange themselves into a body-centered cubic beta structure.

[0006] Commercially pure titanium is similar in physical properties tosteel. However, by addition of other elements, the resultant titaniumalloys are converted to materials having unique characteristics,including high strength and stiffness, corrosion resistance and usableductility. The type and quantity of alloy addition determines themechanical and, to some extent, the physical properties of titanium.

[0007] Commercially pure titanium and its alloys are used in theaerospace industry and in other contexts where corrosion resistance isrequired. Titanium's corrosion resistance is based upon its reactivenature, i.e, it has the ability to form, upon exposure to theatmosphere, a tight, tenacious oxide film that is resistant to a widevariety of media which would corrode other metals. Thus, titanium isresistant to chlorides and oxidizing agents such as nitric acid, and isimmune to environmental corrosion.

[0008] It is known that heat treatment of relatively small pieces ofsubstantially pure titanium can create surface changes giving apleasing, decorative, faceted appearance. For example, U.K. Patent No.1,175,355 describes the surface treatment of titanium, in the context ofdecoration of deep drawn thimbles. In this process, the titanium objectsare heated either under vacuum or in an inert gaseous atmosphere at atemperature of 900-1200° C. for at least five minutes to cause grainenlargement and a faceted surface effect. Thereafter, the heat-treatedtitanium is subjected to an anodizing process. Swiss Patent No. 513,012is also directed to the heat treatment of small titanium objects.

[0009] While surface decoration of such small titanium items is known,no processes have been developed for surface recrystallization of largesheet-like members such as architectural panels. Direct adoption of theprior art techniques described above is entirely unsatisfactory, owingto the fact that the heat treatment tends to substantially warp thelarger panels to the point that they are rendered unusable.

[0010] There is accordingly a need in the art for improved processes andproducts whereby large sheet-type architectural and similar panels canbe provided. Such decorative panels could be used as the facia claddingof buildings and other structures, to provide not only a pleasingaesthetic appearance, but also to give a highly durable, corrosionresistant exterior.

SUMMARY OF THE INVENTION

[0011] The present invention overcomes the problems outlined above andprovides relatively large architectural panels or sheets which aredesigned for, e.g., attachment to the exterior surfaces of buildings orother structures; the panels are treated to give various stages ofrecrystallization to thereby create visually impressive aestheticdesigns. Broadly speaking, such panels are generally quadrate inconfiguration and are formed of substantially pure (normally at least99% pure) titanium. Moreover, they have a length or width dimension ofat least about 3 inches, and preferably substantially larger (on theorder of at least about 24 inches), with at least one face of the panelbeing heat-recrystallized and having an oxidation coating over therecrystallized face. Under certain processing conditions, the panels mayalso assume an undulating shape which further increases the aestheticeffect.

[0012] In terms of the heat treatment method, it has been found that thearchitectural panels must be subjected to multiple, controlled ovenheating steps with intermediate cooling between the heating steps so asto effect the desired grain growth and recrystallization of surfaceportions of the panel. During such multiple heating steps, at least aportion of the circumscribing margin of the panel is restrained,preferably through the use of a frame disposed substantially around themargin to inhibit moving thereof during heating. The frame normallyincludes a plurality of interconnected frame members cooperativelyextending about substantially the entirety of the panel margin, with theframe members being formed of a material different than titanium andpreferably selected from the group consisting of high temperatureceramics and molybdenum. In order to further rigidify the panel andframe assembly, stiffening elements may be inserted proximal to thecorners of the panel, preferably adjacent the rear surface thereof.

[0013] The heating steps are preferably carried out under vacuumconditions typically on the order of 10⁻³ to 10⁻⁵ torr. The particularheating regimen employed is variable depending upon the size of thepanel and the desired surface decoration. Generally speaking though, themultiple heating steps involve relatively rapid heating up to a maximumtemperature range above the transition temperature of the titanium,whereupon this maximum temperature range is maintained for a period oftime. Where two heating steps are employed, the second maximumtemperature range is normally somewhat lower than the first maximumtemperature range, but the second range is maintained for asubstantially longer period of time as compared with the first timeperiod.

[0014] Intermediate cooling on the other hand preferably includes thestep of injecting an inert cooling gas into the oven, with argon beingvery suitable for this purpose. After a minimum temperature range isreached using inert gas cooling, the gas is removed and vacuumconditions reestablished for the next heating step.

[0015] After the recrystallization multiple heating steps are concluded,the panels may then be oxidized in air if an interference color isdesired. Different time-temperature heating in air produces differenttypes and intensities of coloration on the panels, which can becontrolled for predetermined effect.

[0016] During fabrication, individual panels are first framed and arethen suspended in spaced relationship from each other using a graphiteand molybdenum hanger assembly. The entire hanger assembly withinstalled framed panels is then placed within a heating oven forrecrystallization heating and oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a plan view of a preferred, decorative architecturaltitanium panel in accordance with the invention, illustrating thereverse-bend marginal attachment flanges of the panel;

[0018]FIG. 2 is a fragmentary side elevational view of the righthandmargin of the panel depicted in FIG. 1;

[0019]FIG. 3 is a fragmentary side elevational view of the lefthandmargin of the panel depicted in FIG. 1;

[0020]FIG. 4 is a vertical sectional view taken along line 4-4 of FIG. 1and illustrating the upper and lower reverse bend marginal attachmentflanges;

[0021]FIG. 5 is a front elevational view of a multiple-panel assemblyused to support a plurality of individual titanium architectural panelsduring heat treatment thereof;

[0022]FIG. 6 is a side elevational view of the multiple-panel assemblyof FIG. 5;

[0023]FIG. 7 is a fragmentary side view of one of the framed titaniumarchitectural panels supported on the multiple panel assembly of FIGS. 5and 6;

[0024]FIG. 8 is a perspective view of one of the preferred corner gussetstiffening elements used as a part of the frame for each architecturalpanel;

[0025]FIG. 9 is a fragmentary exploded perspective view illustrating thepreferred construction of the frame elements and the method ofinterconnection thereof;

[0026]FIG. 10 is a graph of temperature versus time depicting anexemplary time-temperature profile during heat treatment of the titaniumpanels in accordance with the invention; and

[0027]FIG. 11 is a comparative scanning electron microphotograph (SEM)illustrating a titanium sheet prior to heat treatment in accordance withthe invention (right side of photograph) and a similar SEM depicting atitanium sheet after heat treatment (left side of photograph), showingthe change in surface crystal structure from the heat treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] The preferred apparatus for use in preparing the decorativetitanium panels of the invention is illustrated in FIGS. 1-9. Inparticular, the goal is to provide a plurality of titanium panels 20 ofdesired size for an architectural application. Generally speaking, suchpanels will be substantially quadrate in plan configuration, and wouldtypically have a minimum length or width dimension of at least about 3inches and a thickness of from about 0.005-0.250 inches; morepreferably, the panels are substantially square or rectangular and wouldhave a minimum length or width dimension of at least about 12 inches(and most preferably at least about 24 inches), and a thickness of fromabout 0.020-0.125 inches. The panels 20 are formed of substantially puretitanium, usually commercial Grades 1-4. The most preferred titanium isa Grade 1 material having mechanical properties specified in ASTM B265,with the following ingredients apart from titanium: oxygen equivalent,0.05-0.10 (aim 0.075); hydrogen, 0.015 max; oxygen, 0.07 max; carbon,0.02 max; iron, 0.07 max; nitrogen, 0.012 max; other elements, each,0.10 max; and other elements, total 0.30 max.

[0029] The factory-delivered titanium material used in the fabricationof the panels 20 usually has been acid-pickled using a mixture ofhydrofluoric and nitric acids, followed by a rinse with distilled waterand a squegee/air knife treatment. The material has a PVC film appliedto one face, and is coiled for shipment. At the fabrication site, thetitanium is cut to size, the PVC film is removed, and fabricated asdescribed in detail hereafter.

[0030] Referring to FIG. 1, it will be seen that the exemplary panel 20is substantially square in plan configuration presenting a front surface22 and an opposed rear surface 24. The panel is equipped with fourreverse-bend marginal flanges, namely rear surface flanges 26 and 28which are in adjacency at sharp corner 30, as well as front reverse-bendflanges 32 and 34. It will be observed that the remaining three corners36, 38, 40 of the panel 20 are oblique. The flanges 26, 28 and 32, 34are designed so as to permit interengagement and attachment of thepanels 20 on the exterior surface of a building or the like.

[0031] In order to prepare the panels 20 for heat treatment inaccordance with the invention, they are first placed within a frameassembly 42 made up of four interconnected molybdenum frame elements 44,46, 48 and 50 which frictionally engage corresponding side margins ofthe panel 20 as well as the flanges 26, 28, 32, 34. Referringspecifically to FIG. 9, it will be seen that the uppermost frame element46 includes a depending, U-shaped section 52 as well as laterallyprojecting, upper suspension segments 54 and an uppermost lip 56. Theside marginal elements 44 and 48 are similarly constructed, and have aprimary U-shaped body 58 with openings 60 and 62 at the upper and lowerends thereof, and upper and lower lips 64, 66 respectively. The lowerelement 50 is a simple U-shaped member as shown.

[0032] The frame elements are pressed over the corresponding sidemargins and flanges of the panel 20 by first inserting the free leg ofU-shaped section 52 into the confines of upper panel flange 34 (seeFIGS. 7 and 9), whereupon the lower element 50 is pressed over the lowerflange 26. At this point the side elements 44 and 48 are slid over thelateral projections 54 and into engagement with flanges 32 and 28, sothat a portion of the projections 54 extend through the openings 60beyond the side frame elements 44 and 48. Simultaneously, the ends ofthe element 50 are received within the lower openings 62. Of course, theupper and lower lips 64 and 66 assist in preventing inadvertentdislodgement of the frame elements. The frame assembly 42 is completedby insertion of four generally triangular gusset plates 68 each having ahandle 70 between the rear surface 24 of panel 20 and the adjacentsections of the frame elements, i.e., the triangular face of each gusset68 is in contact with the rear surface 24.

[0033] The framed panels 20 are thus structurally self-sustaining andare ready for heat treatment. In this connection, use of the frameassemblies 42 is important in the manufacture of the finished panels, soas to avoid edge warpage or distortion. At the same time, use of suchframing does not detract from the desirable surface recrystallization offront panel surface 22.

[0034] In order to better handle a plurality of the framed panels 20,use is made of a hanger assembly broadly referred to by the numeral 72.This assembly includes a lowermost metal (Inconel) grid-like support 74having a pair of fore and aft extending, laterally spaced apart basebeams 75 thereon. The beams 75 support laterally extending crossbeams 76which in turn support and are connected to four uprights 77. In thisrespect, it will be seen that molybdenum connector plates 78 areemployed to interconnect the crossbeams 76 and uprights 77. The upperends of the uprights 77 support fore and aft extending beams 80.Finally, it will be observed that the crossbeams 76 also support a totalof four, fore and aft extending beams 84. Preferably, the beams 75 and76, uprights 77, and beams 80, 84 are formed of graphite. In addition,it will be seen that the upper beams 80 are equipped with a series ofupstanding spacer pin pairs 86 and that the inboard lower beams 80 havea similar series of upwardly projecting pin pairs 88.

[0035] The framed panels 20 as individual panel units are supported onhanger assembly 72 by means of the laterally extending projections 54 ofthe upper frame elements 46. As best seen in FIG. 5, such projectionsrest atop the upper beams 80 so that the individual framed panels dependtherefrom. Proper spacing of the framed panels is provided by means ofthe upper and lower pins 86, 88, i.e., the upper portion of each frameelement 46 is located between a corresponding pin pair 86, while thelower frame element 50 (and thus the lower margin of the panel 20) iscaptively retained between a lower pin pair 88. Once all of the framedpanels 20 are positioned on the hanger assembly, the entire assembly canthen be placed within an appropriate oven or furnace for heat treatment.

[0036] The following example sets forth the steps employed in apreferred process for creation of decorative titanium architecturalpanels in accordance with the invention. It is to be understood,however, that this example is provided by way of illustration only andnothing therein should be taken as a limitation upon the overall scopeof the invention.

Example

[0037] A total of 30 molybdenum-framed architectural panels 20 suspendedfrom graphite hanger assemblies 72 were prepared as described above. Thehanger assemblies 72 with the framed panels 20 in place were forkliftedinto a tubular electric oven for heat treatment. In the first step, theoven door was closed and the oven was evacuated to a level of about 10⁻⁴torr over a period of about 10 minutes. At this point, the heating cyclewas commenced to give first and second heating steps with anintermediate cooling step, sufficient to recrystallize the panels 20(and particularly the front surfaces 22 thereof) for decorative effect.The time-temperature profile of this heat treatment is set forth in FIG.10.

[0038] In particular, during the first heating step H₁, the temperatureof the oven was rapidly elevated to achieve a first maximum temperaturerange T_(H1) of 2000-2400° F., which was maintained for a period ofabout 5 minutes. At the end of this step H₁, the first cooling step C₁was performed. This involved repressurization of the oven by injectionof argon into the oven to achieve a pressure of 1-2 bar therein. Thisresulted in rapid oven temperature loss down to a first minimumtemperature range of T_(L1). This was accomplished over a period of 50minutes to achieve a minimum temperature range of 200-250° F.Thereafter, the oven was again evacuated and a second heating step H₂was carried out. This involved reheating the oven along the depictedprofile to achieve a second temperature maximum T_(H2) of 2000-2400° F.,which was maintained for a period of 60 minutes.

[0039] At the end of the second heating step, argon was again injectedduring the second cooling step C₂, causing rapid oven temperature lossdown to a second minimum temperature range T_(L2) of 200-250° F. At thispoint, the oven was used to oxidize the panels. This involvedintroduction of ambient air into the oven followed by heating to atemperature of about 530° F. for a period of 60 minutes in order to forma tenacious oxidation layer over the titanium panels. At the end of thisoxidation step, the oven was again cooled and the completed panels werethen removed from the oven. The molybdenum frames were removed from eachpanel, and the latter were covered with protective PVC film material,ready for shipping and use.

[0040]FIG. 11 is a comparative SEM depicting surface portions of anuntreated titanium sheet and a sheet treated in accordance with theinvention. As illustrated in the left side of the figure, the heattreatment effects a significant change in surface crystal structurewhich is responsible for the desirable aesthetic effect of architecturalpanels produced pursuant to the invention.

[0041] It will be appreciated that the recrystallization procedure canbe carried out over a range of values in terms of maximum and minimumtemperature ranges, heating and cooling rates, vacuum conditions andargon pressures, and that similarly the final oxidation step can bevaried. The following table sets forth broad and preferred ranges forthese steps. TABLE Recrystallization Treatment First Heating Step (H₁)Broad Range Preferred Range Maximum Temperature Range (° F.) 2000-24002100-2300 Heating Rate (° F./min) 15-40 20-30 Vacuum Conditions (torr)10⁻³ to 10⁻⁶ 10⁻³ to 10⁻⁵ Maximum Temperature Range Maintenance (min) 3-60 15-40 First Cooling Step (C₁) Minimum Temperature Range (° F.) 75-300 200-250 Cooling Rate (° F./min) 35-80 40-60 Argon Pressure (bar)0.75-3   1-2 Minimum Temperature Range Maintenance (min) 10-70 20-50Second Heating Step (H₂) Maximum Temperature Range (° F.) 1800-24002000-2300 Heating Rate (° F./min) 15-40 20-30 Vacuum Conditions (torr)10⁻³ to 10⁻⁶ 10⁻³ to 10⁻⁵ Maximum Temperature Range Maintenance (min) 30-180 40-80 Second Cooling Step (C₂) Minimum Temperature Range (° F.) 75-300 200-250 Cooling Rate (° F./min) 35-80 40-60 Argon Pressure (bar)0.75-3   1-2 Minimum Temperature Range Maintenance (min) 10-70 20-50Oxidation Temperature (° F.) 400-700 475-575 Time (min) 40-90 50-70

I claim:
 1. A method of preparing a decorative titanium panel,comprising the steps of: providing a panel having an area to bedecorated and a circumscribing margin about said area, said panel formedof substantially pure titanium; and subjecting said panel to multipleoven heating steps with intermediate cooling between the heating steps,sufficient to recrystallize surface portions of said area.
 2. The methodof claim 1, including the step of restraining at least a portion of saidmargin during said multiple heating steps.
 3. The method of claim 2,said restraining step comprising the steps of positioning a framesubstantially about said margin to inhibit movement of said marginduring said multiple heating steps.
 4. The method of claim 3, said framecomprising a plurality of interconnected frame members cooperativelyextending about substantially the entirety of said margin.
 5. The methodof claim 3, said frame formed of a material different than titanium andbeing shape-retaining during said multiple heating steps.
 6. The methodof claim 5, said frame formed of a material selected from the groupconsisting of molybdenum and high temperature ceramics.
 7. The method ofclaim 3, said panel being substantially quadrate in plan configuration,said frame comprising four frame members interconnected adjacent thecorners of said quadrate panel, said frame-positioning step furtherincluding the step of inserting stiffening elements proximal to each ofsaid corners.
 8. The method of claim 1, including the step of carryingout each of said heating steps under vacuum conditions.
 9. The method ofclaim 8, said vacuum conditions being a pressure of from about 10⁻³ to10⁻⁵ torr.
 10. The method of claim 1, including the step of injecting aninert cooling gas into said oven between said multiple heating steps.11. The method of claim 10, said inert gas comprising argon.
 12. Themethod of claim 1, there being first and second heating steps with acooling step following each heating step.
 13. The method of claim 12,said first heating step comprising heating said oven to a first maximumtemperature of from about 2000-2400° F., and maintaining said firstmaximum temperature for a period of from about 3-60 minutes.
 14. Themethod of claim 13, said period being from about 15-40 minutes.
 15. Themethod of claim 12, said first heating step being carried out so as toraise the oven temperature at a rate of from about 15-40° F. per minute.16. The method of claim 15, said rate being from about 20-30° F. perminute.
 17. Then method of claim 12, including the step of injecting aninert gas into said oven to effect cooling thereof, after said firstheating step.
 18. The method of claim 17, said cooling being carried outso as to lower the oven temperature at a rate of from about 35-80° F.per minute.
 19. The method of claim 18, said rate being from about40-60° F. per minute.
 20. The method of claim 17, said cooling stepbeing carried out to lower the oven temperature to a temperature of fromabout 75-300° F.
 21. The method of claim 20, said temperature being fromabout 75-200° F.
 22. The method of claim 12, said second heating stepcomprising heating said oven to a second maximum temperature of fromabout 1800-2400° F., and maintaining said second maximum temperature fora period of from about 30-180 minutes.
 23. The method of claim 22, saidsecond maximum temperature being from about 2000-2300° F.
 24. The methodof claim 22, said second heating step comprising heating said oven tosaid second maximum temperature at a rate of from about 15-40° F. perminute.
 25. The method of claim 24, said rate being from about 20-30° F.per minute.
 26. The method of claim 22, including the step of injectingan inert gas into said oven to cool the oven after said second heatingstep.
 27. The method of claim 26, said cooling being carried out so asto lower the temperature of said oven to a temperature of from about75-300° F.
 28. The method of claim 27, said temperature being from about200-250° F.
 29. The method of claim 26, said cooling being carried outso as to lower said oven temperature at a rate of from about 35-80° F.per minute.
 30. The method of claim 29, said rate being from about40-60° F. per minute.
 31. The method of claim 1, including the step ofoxidizing said panel after said multiple heating steps.
 32. The methodof claim 31, said oxidizing step comprising the step of heating saidpanel in an oven with air therein to an oxidizing temperature range offrom about 400-700° F., and maintaining the oven temperature within theoxidizing temperature range for a period of from about 40-90 minutes 33.A method of preparing a decorative titanium panel comprising the stepsof: providing a generally quadrate panel having marginal edges, aminimum length or width dimension of at least about 3 inches, and athickness of from about 0.005-0.250 inches, said panel being formed ofcommercially pure titanium; framing said panel by placing interconnectedframe elements about the marginal edges of the panel, said elementsbeing formed of a material different than said titanium and havingsufficient rigidity to inhibit movement of said edges during heating ofthe panel; placing said framed panel within an oven; reducing thepressure within said oven to a level of from about 10⁻³-10³¹ ⁶ torr;rapidly heating the oven to a first maximum temperature range within therange of from about 2000-2400° F., and maintaining said first maximumtemperature range for a period of from about 3-60 minutes; rapidlycooling the oven to a first cool temperature range within the range offrom about 75-300° F., said cooling including the steps of reducing thevacuum conditions within said oven and injecting an inert cooling gasinto the oven; thereafter rapidly heating the oven to a second maximumtemperature range within the range of from about 1800-2400° F. andmaintaining said second maximum temperature range for a period of fromabout 15-40 minutes; and again rapidly cooling the oven, and thereafterremoving the framed panel from the oven.
 34. The method of claim 33,including the step of oxidizing said panel after the last cooling step.35. The method of claim 34, said oxidizing step comprising the step ofheating said panel in an oven with air therein to an oxidizingtemperature range of from about 400-700° F., and maintaining the oventemperature within the oxidizing temperature range for a period of fromabout 40-90 minutes.
 36. The method of claim 33, said frame elementsformed of molybdenum.
 37. A titanium panel unit adapted for heattreatment in order to form a decorative, recrystallized area on thetitanium panel, said unit comprising: a panel having an area to bedecorated and a circumscribing margin about said area, said panel formedof substantially pure titanium; and a frame disposed substantially aboutsaid margin in order to inhibit movement of the margin during heattreatment, said frame comprising frame elements in contact with saidmargin and formed of a material selected from the group consisting ofhigh temperature ceramics and molybdenum.
 38. The unit of claim 37, saidpanel being substantially quadrate in plan configuration, said framecomprising four frame elements interconnected adjacent the corners ofsaid quadrate panel, said frame further including stiffening elementsproximal to each of said corners.
 39. The unit of claim 38, saidstiffening elements comprising generally triangular gusset members inface-to-face contact with a surface of said panel remote from said area.40. A multiple-panel assembly adapted for placement within an oven forheat treatment of the panels, said multiple-panel assembly comprising: aplurality of titanium panel units adapted for heat treatment in order toform a decorative, recrystallized area on the titanium panel, each ofsaid units comprising a panel having an area to be decorated and acircumscribing margin about said area, said panel formed ofsubstantially pure titanium; and a frame disposed substantially aboutsaid margin in order to inhibit movement of the margin during heattreatment, said frame comprising frame elements in contact with saidmargin and formed of a material selected from the group consisting ofhigh temperature ceramics and molybdenum; and a hanger assembly holdingsaid panel units in generally aligned, spaced apart relationship. 41.The assembly of claim 40, each of said panels being substantiallyquadrate in plan configuration, each of said frames comprising fourframe elements interconnected adjacent the corners of a correspondingquadrate panel, said frame further including stiffening elementsproximal to each of said corners.
 42. The assembly of claim 41, saidstiffening elements comprising generally triangular gusset members inface-to-face contact with a surface of each of said panels remote fromthe corresponding area.
 43. The assembly of claim 40, said hangerassembly including a series of uprights supporting side marginalstringers, each of said units extending between and being supported bysaid side marginal stringers.
 44. The assembly of claim 43, saiduprights and stringers formed of graphite.
 45. A decorativearchitectural panel comprising a generally quadrate panel formed ofsubstantially pure titanium and having a minimum length or widthdimension of at least about 3 inches and a circumscribing margin, atleast one face of said panel being heat-recrystallized with an oxidationcoating over said at least one face.
 46. The panel of claim 45, saidmargin presenting four substantially rectilinear edges, each such edgedefined by a reverse bend flange.
 47. The panel of claim 46, two of saidflanges being located adjacent one face of said panel, with the othertwo flanges located adjacent the opposite face of the panel.
 48. Thepanel of claim 45, said panel presenting an undulating configurationbetween said circumscribing margin.